IC tags with IDs that can be identified by contactless means have been used in many different fields, such as merchandise recognition, individual attestation, and forgery prevention of banknotes or negotiable securities, and are now more widely utilized in extended fields, such as production lines and distribution of goods.
Especially, by affixing IC tags to items, a big effect is expected in not only product processing and distribution control, but also inventory control
To achieve accurate and prompt inventory control, it is desired that items be automatically located.
In order to have items automatically located, it is necessary to allocate an interrogator (RFID interrogator) at each and every inventory location, providing 1 to 1 correspondence between the interrogator and the inventory location, so as to recognize the inventory location by the interrogator's individual address.
Alternatively, an antenna can be allocated at each and every inventory locations having 1 to 1 correspondence between the antenna and the inventory location so as to recognize the inventory location by the antenna's individual address.
When searching an item in a particular inventory location, the address of its interrogator or antenna is specified and IDs of items therein are read.
When searching an inventory location where a particular item is placed, the addresses of interrogators or antennas are sequentially designated and all IDs of items in each inventory location are respectively read. The inventory location can be recognized from the address of an interrogator or an antenna being designated when target ID is detected.
Disadvantageously, however, interrogators use the same frequency and thus mutual interference would occur and disturb communication when multiple interrogators are closely allocated. Further disadvantageously, when reading IDs of items per designated antenna, radio waves would reach adjacent inventory locations and IDs of items therein would be mistakenly read.
To prevent such misreading, it is necessary to deliberately shield the inventory locations from each other, but this results in increasing restrictions on the inventory locations.